It is known that reduced coenzyme Q10 can be prepared by producing coenzyme Q10 in the conventional manner, for example by synthesis, fermentation, or extraction from natural products, and concentrating a reduced coenzyme Q10-containing eluate fraction resulting from chromatography (JP-A-10-109933). On that occasion, as described in the above-cited publication, the chromatographic concentration may be carried out after reduction of oxidized coenzyme Q10 contained in the reduced coenzyme Q10 with a reducing agent such as sodium borohydride or sodium dithionite (sodium hyposulfite), or reduced coenzyme Q10 may be prepared by reacting the reducing agent mentioned above with an existing highly pure grade of coenzyme Q10.
JP-A-57-70834 discloses an example in which reduced coenzyme Q10 was synthesized by dissolving coenzyme Q10 in hexane and adding an aqueous solution of sodium hydrosulfite (sodium hyposulfite) in an amount of twice the weight of coenzyme Q10 to the solution, followed by stirring.
However, the present inventors preliminary investigated the above reduction method, and found that it is not so easy to obtain a high-quality reduced coenzyme Q10 in a high yield.
The above problem leads to not only economical disadvantageous but also to problems in qualities such as the immixture of oxidized coenzyme Q10, which is difficult to remove, into a product. Moreover, use of a large amount of a reducing agent enhances the load for removal and detoxification of the reducing agent and components derived therefrom.
Thus, the above disadvantages in the reduction reaction give rise to a necessity of another process for purification.